Timri has put it very well, and I totally agree with that.
None of the decisions we are now faced with are comfortable ones.
If we do nothing, ISIS will continue their campaigns regardless.
If we bomb them in Syria, they will still continue but we might be able to weaken and disrupt their main command structure and training camps. At least we would be taking action, and something needs to be done.
When our Parliament voted against action in Syria a couple of years ago (was it?) I must say I was relieved, as I thought Blair and Bush had acted like a pair of fuckwits going into Iraq on trumped up suppositions of Weapons of Mass Destruction, and without any plan in mind for what was to be done once Saddam Hussein had been removed from power. I wanted no more of it.
Having spent last weekend in Paris visiting my student DD1 (booked and planned weeks before), I have changed my mind regarding action against ISIS in Syria. They must be tackled. I don't like it, and I am aware that there will be loss of life and collateral damage. I don't say any of it lightly, but I really cannot see what other realistic options there are. Surely we cannot just let things go on as they are.